Closed wrench openings conventionally include planar engagement surfaces for engaging each side of a nut or bolt head to be torqued. Usually such planar engagement surfaces are arranged in either a hexagonal arrangement that is conventionally referred to as a six point opening or are arranged in a double hexagonal arrangement that is conventionally referred to as a twelve point opening. In either case, tolerances adopted by wrench manufacturers and by manufacturers of nuts and bolts result in some spacing between the planar engagement surfaces of a wrench opening and the sides of a nut or bolt head to be torqued. Such spacing results in a certain amount of "free swing" that will vary depending upon the particular size of each wrench opening and the size of the nut or bolt head received by the opening. The net result is that there is normally a line contact between the linear side junctions of a nut or bolt head and the planar engagement surfaces of a wrench opening applying the torque. This line contact amplifies the stress applied to the nut or bolt head and thereby results in deformation and less torquing ability than would be the case if the stress were distributed by surface-to-surface engagement.
In an attempt to overcome the above mentioned problems, prior closed wrench openings have included angularly oriented planar engagement surface portions whose angularity is selected in attempt to provide a surface-to-surface engagement with the nut or bolt head when the mean tolerance spacing is present. However, a greater or lesser extent of spacing will still result in the line contact that distorts the nut or bolt head and prevents a greater application of torque than would be possible with surface-to-surface engagement. Prior art patents which disclose closed wrench openings having angularly oriented planar engagement surface portions include U.S. Pat. Nos.: 3,242,775 Hinkle; 3,466,956 Bowers; 3,495,485 Knudsen et al; 3,903,764 Andersen; 3,908,488 Andersen; and 4,512,220 Barnhill, III, et al.
Other wrenches noted during the investigation involving the present invention are disclosed by U.S. Pat. Nos.: 736,687 Chandler; 1,954,141 Miquelon; 2,652,735 Wilder; 2,685,219 Diebold; 2,692,522 Reyner; 3,577,817 Smith; and 4,253,353 Symbol.